A subscription model

[harshraj22]

Add a subscription model. An existing user can have one of the following subscription tiers:

• Free (30 requests per 24 hour)
• Basic (150 requests per 24 hour)
• Advanced (500 requests per 24 hour)

The limit on the number of API calls by a user should be limited by the type of subscription they own.

[harshraj22]

Can use reddis to implement it from scratch[1], [2] or use a third party library.

Read More: nordicapis

# docker run -p 6379:6379 --name redis_server redis:4-alpine
import redis

r = redis.StrictRedis(host='localhost', port=6379, decode_responses=True, password="")
print('Ping:', r.ping())
print(r)
print('setting:', r.set("key", "value"))
print('getting:', r.get("key"))

import time

username = 'user1'

WINDOW_LENGTH = 2 # in Seconds
for _ in range(3):
    cur_time = time.time()
    r.zadd(username, {cur_time: cur_time})
    time.sleep(1) # Sleep for 1 Second

p = r.pipeline()
p.zremrangebyscore(username, 0, time.time() - WINDOW_LENGTH)
cur_time = time.time()
p.zadd(username, {cur_time: cur_time})
p.expire(username, WINDOW_LENGTH)
p.execute()

print(r.zrange(username, 0, -1))

[harshraj22]

A potential Architecutre:

Might have to deal with Distributed Commit 😨

The three Major components for this would be:

• Consistency across DBs
• Rate Limit On user request based on subscription tier they belong to
• Integration of the payment gateway

[harshraj22]

Read about saga pattern and 2 phase commit

Another helpful stackoverflow thread.

[harshraj22]

The subscription based Rate Limiting should be developed as a separate and completely independent identity, which is easy to plug in into any existing product. Is should not be tightly coupled with existing product.

A possible Architecture:
Subscription Rate Limiter is a library that accept details to connect to existing Redis and MySql Server. It has methods to update the MySql and Redis server and Query them. It should be made in such a way that Replacing MySql Server with any other database is easy.

Similarly Data Monitoring Service can also be separated out into an independent project.

[harshraj22]

Flow for Rate Limit On user request based on subscription tier they belong to:

• Payment microservice exposes and endpoint to update the redis cache from the mysql database.
• A short lived microservice updates the redis cache once the payment microservice is up
• The Subscription microservice starts, and uses the cache to rate limit based on the number of requests and the subscription tier the user belongs to.